Not really for King Triton, besides aren't the VAST majority of the Disney worlds don't know about the existence of other worlds and the Keyblade War.
Which I'm going to say it again, it just made King Triton's knowledge of the Keyblade "forced" regardless of it, even after the release of the first KH game, which baffles why the Development team didn't even bother putting Atlantica in Birth by Sleep and/or X/Union X. :/
The vast majority of the population of the Disney worlds don't know about the existence of other worlds. The same way that Mickey visited Ansem The Wise in Radiant Garden, someone could have done that for King Triton. Someone could have attacked Atlantica in the past with a keyblade. We don't know. Clearly something happened that made him weary of Sora and his keyblade.
Beast, Belle, Jasmine (her own father the Sultan -- if he was ever shown -- probably doesn't know other worlds exists), Aladdin, Genie, Mushu, King Triton, Ariel, Jack Skellington, Sandy Klawz, Simba, Tinkerbell, Peter Pan, Alice, Cinderella, Aurora, Snow White, Minnie, Daisy, Bambi, Dumbo, Chicken Little, and Stitch know that other worlds exist. Just because they know other worlds exist doesn't mean that they're going to announce it to everyone in their world. Jasmine didn't even bring it up (or the events of KH1 outside of Agrabah) in KH2. Mushu didn't tell Mulan where he fought alongside Sora. Simba doesn't even seem to care to remember in KH2. Neither do Beast or Belle.
The development team don't have to show a world in the past and explain how a certain character knows something, especially something that can be explained away in one line. If they ever go back to Atlantica and want to expand on it, Triton can simply say "a keyblade wielder visited Atlantica once and I had to stop him from destroying the world". Maybe they can even have the keyblade wielder be a land dweller that dove down into Atlantica, which would explain his hatred for land dwellers (maybe even make it the MoM).